This invention relates to a contactless proximity switch apparatus and an arrangement for mounting the same. Such contactless proximity switch and mounting arrangement are especially advantageous for use with work cylinders where it is required to detect the position of the piston within the work cylinder. To date, a typical work cylinder having a reciprocally moveable piston disposed therein employed an element disposed inside the cylinder and usually mounted such element on the piston itself to act as a portion of the piston position determining arrangement. An example of such an approach can be found in the German Pat. No. DE 29 17 232, where a reed contact switch disposed on the cylinder jacket was activated when a magnet element, secured to the piston head, came into proximity to thus close the contacts of the reed switch. The disadvantage of such an approach is that the internal layout of the piston and rod structure must be modified to accommodate placement of the magnetic element, which placement requires additional space and interferes with the piston movement. Still other proximity switch devices employ a contoured jacket which fits over the cylinder and employs either a resistance or inductance measuring arrangement to determine the position of the piston; in this situation, the external jacket portion must be precisely contoured to the shape of the cylinder, such precision-contoured jacket being required in as many different sizes as there are different-sized cylinders.